Robert - that 56T Mantle is a really great looking card. Definitely would not look out of place in a higher grade!
Here are a couple recent additions. First I'm a sucker now for centered Mantles. Already have a psa 5.5, but this one looks darn near as good and better centered. 53 Bowman I believe may be the most undervalued Mantle there is just comparing the numbers on the pop report...
Also I finally got outside my comfort zone and bought something other than Mantle. I am leaning towards either starting a Maris run, or dappling in the rookie category. Haven't decided yet Maris may be better for my wallet though...